The Role of Magnetic Resonance Imaging in the Differential Diagnosis of Giant Rectal and Perirectal Masses

Introduction: Our purpose was to depict some specific qualitative and quantitative magnetic resonance imaging (MRI) and diffusion weighted imaging (DWI) findings in differential diagnosis of huge tumors of rectum and perirectal region. Methods: A total of 81 patients who had >= 5 cm huge tumors of rectum and perirectal region [36 (44%) women and 45 (56%) men] with a mean age of 54 +/- 15 (standard deviation) were enrolled in this retrospective study. Pre-operative MRI with DWI examinations of patients were reviewed by an experienced radiologist. Qualitative (signal intensity, contrast enhancement pattern, the existence of lymphadenopathy and metastasis) and quantitative imaging findings were statistically analyzed according to histopathological results. Results: Of 81 huge tumors of rectum and perirectal region, 60 were malignant and 21 were benign. Among (n=60) malignant tumors, there were 48 rectal adenocancers, two prostate adenocancers, three leiomyosarcomas, three ovarian cancers and four rectal gastrointestinal stromal tumors (GISTs). All rectal GISTs (n=4) showed peripheral heterogeneous arterial enhancement and had hypointense peripheral components whereas central components were more heterogeneous and iso-/hyper-intense on T2-weighted sequences. Most of rectal adenocancers (41/48, 85%) showed significant enhancement. Lymphadenopathy, invasion and far metastasis were only observed in malignant tumors. Mean "apparent diffusion coefficient" (ADC) ratios of malignant tumors (0.56 +/- 0.10) were significantly lower than those of benign tumors (0.95 +/- 0.21) (p<0.05). Conclusion: Specific MRI findings combining with ADC ratio estimation can be helpful for differential diagnosis of bulky rectal and perirectal tumor, and appropriate management of patient.